Page:Proceedings of the Royal Society of London Vol 60.djvu/232

212 Less diffusible portion— Volume of globe..................... 162*843 c.c. Pressure at filling......... 663*8 mm. Temperature......................... 19*93° Weight ................... ..... 0*02902 gram Density.................................. 2*452

The less diffusible portion was next subjected to the process of removing nine-tenths, the remaining tenth being collected apart. This process was repeated three times, so that any portion of gas less diffusible than the main bulk should thus be left as a residue. From the more diffusible portion nine-tenths was also diffused out. The more diffusible portions were then mixed, and the density was again determined.

Volume of globe..................... 162*843 c.c. Pressure at filling .................. 765*7 mm. Temperature ......................... 20*98° Weight. ................................. 0*02801 gram Density ............................... 2*057

This number is practically identical with that previously obtained, viz., 2*049.

It was of interest to follow the less diffusible gas, so as to ascertain what impurity caused its higher density. Another set of fractionations was therefore carried out, and after five separate processes, in each of which a residue was left, and that residue further diffused, so as to separate all light gas as completely as possible, a few c.c. of gas were collected, in which the spectrum of argon was strong. Now we are certain that at no stage in the operations was any considerable quantity of air admitted by leakage. It may safely be said that the total amount of air could never have exceeded 5 c.c. And inasmuch as the density of samples of helium from various sources, which had undergone very little handling, differed by small amounts, varying between 2*114 and 2*181, this must be ascribed to contamination with argon, contained in the mineral from which the helium had been obtained. Every effort was made to detect any unknown lines in the spectrum of the residue, but in vain. With the jar and spark-gap, the blue spectrum of argon was visible, and was compared with that from a standard tube.

If thus the increased density is due to argon, it is possible to calculate the proportion of the latter; first, in the lightest gas of density 2*117 found in samarskite; second, in the residue in which the argon had been concentrated, possessing the density 2*452, on the assumption that helium possesses the density 2*042. The first must contain 0*42 per cent, of argon ; the second, 2*28 per cent.